Amine-containing materials such as amine-containing analytes, amino acids, DNA fragments, RNA fragments, protein fragments, organelles, and immunoglobins immobilized on the surface of a substrate can be used in numerous applications. For example, immobilized biological amines can be used for the medical diagnosis of a disease or genetic defect, for biological separations, or for detection of various biomolecules.
The attachment of amine-containing materials to a substrate is often achieved through the use of a tethering compound. A tethering compound usually has two reactive functional groups separated by a linking group. One of the functional groups provides a means for anchoring the tethering compound to a substrate by reacting with a complementary functional group on the surface of the substrate. A second reactive functional group can be selected to react with an amine-containing material. The second reactive functional group can be, for example, an activated acyl derivative, such as an N-hydroxysuccinimide ester, or a cyclic azlactone. An amine-containing material can react with the N-hydroxysuccinimide ester to form a carboxamide resulting in the displacement of an N-hydroxysuccinimide fragment. An amine-containing material can react with the cyclic azlactone resulting in an opening of the ring structure.
Although tethering compounds that include a group such as an N-hydroxysuccinimide ester or a cyclic azlactone can be highly reactive with primary amine-containing materials, such tethering compounds can suffer from a number of disadvantages. Many of the reactions with biological amines are conducted in dilute aqueous solutions. Under these conditions, the N-hydroxysuccinimide ester functional group is known to undergo rapid hydrolysis. This competing reaction can cause incomplete or inefficient immobilization of the amine-containing materials on the substrate. While cyclic azlactone functional groups are more stable to hydrolysis, cyclic azlactone groups tend to be synthetically incompatible with many groups that could be used to attach the tethering compound to a substrate.